New research indicates that early Martian volcanoes may have emitted reactive sulfur gases that warmed the planet and supported conditions suitable for microbial life.
Although scientists are still working to understand what Mars was like in its earliest stages, new research points to the possibility that the planet’s atmosphere could have supported life. The study proposes that volcanic eruptions released sulfur gases that helped warm the planet through a greenhouse effect.
The work, published in Science Advances, was carried out by a research team from The University of Texas at Austin.
To explore the chemistry of ancient Mars, the team analyzed the composition of Martian meteorites and used that information to run more than 40 computer simulations. These models tested different temperatures, chemical conditions, and gas concentrations to estimate how much carbon, nitrogen, and sulfur-based gases early Martian volcanoes may have produced.
Their results challenge earlier climate models that assumed high levels of sulfur dioxide (SO₂). Instead, the simulations indicate that volcanic activity on Mars 3-4 billion years ago likely released large amounts of “reduced” sulfur species, which are highly reactive. These included hydrogen sulfide (H₂S), disulfur (S₂), and possibly sulfur hexafluoride (SF6), a greenhouse gas known for its exceptionally strong warming properties.
A Potentially Habitable Environment
Lead author Lucia Bellino, a doctoral student at the UT Jackson School of Geosciences, explained that such conditions could have shaped an unusual environment on early Mars, one that might have been favorable for certain types of life.
“The presence of reduced sulfur may have induced a hazy environment which led to the formation of greenhouse gases, such as SF6, that trap heat and liquid water,” said Bellino. “The degassed sulfur species and redox conditions are also found in hydrothermal systems on Earth that sustain diverse microbial life.”
Previous Mars studies have researched how the release of gases at the surface, often through volcanic eruptions, may have impacted the planet’s atmosphere. In contrast, this study simulated how sulfur changed as it moved throughout geologic processes, including how it separated from other minerals as it was incorporated into magma layers below the planet’s crust. This is important because it gives a more realistic sense of the chemical state of the gas before it’s released at the surface where it can shape the early climate conditions of Mars.
The study also revealed that sulfur may have been frequently changing forms. While Martian meteorites have high concentrations of reduced sulfur, the Martian surface contains sulfur that’s chemically bonded to oxygen.
“This indicates that sulfur cycling – the transition of sulfur to different forms – may have been a dominant process occurring on early Mars,” said Bellino.
A NASA Discovery Supports the Model
Last year, while the team was in the midst of its research, NASA made a discovery that seemed to back their findings. NASA’s Curiosity Mars rover rolled over and cracked open a rock, revealing elemental sulfur. While Mars is known for being rich in sulfurous minerals, it was the first time the mineral had been found in pure form, unbound to oxygen.
“We were very excited to see the news from NASA and a large outcrop of elemental sulfur,” said Chenguang Sun, Bellino’s advisor and an assistant professor at the Jackson School’s Department of Earth and Planetary Sciences. “One of the key takeaways from our research is that as S₂ was emitted, it would precipitate as elemental sulfur. When we started working on this project, there were no such known observations.”
As the team moves forward, they will use their computer simulations to investigate other processes that would have been essential to sustain life on Mars, including the source of water on early Mars, and whether volcanic activity could have provided a large reservoir of water on the planet’s surface. They also seek to understand whether the reduced forms of sulfur may have served as a food source for microbes in an early climate that resembled Earth’s hydrothermal systems.
Mars is far from the Sun, and today, it’s typically cold with an average temperature of -80 degrees Fahrenheit. Bellino hopes that climate modeling experts can use her team’s research to predict how warm the early Mars climate might have been, and, if microbes were present, how long they could have existed in a warmer atmosphere.
Reference: “Volcanic emission of reduced sulfur species shaped the climate of early Mars” by Lucia G. Bellino and Chenguang Sun, 3 September 2025, Science Advances.
DOI: 10.1126/sciadv.adr9635
The research was funded by The University of Texas at Austin Center for Planetary Systems Habitability, the National Science Foundation, and the Heising-Simons Foundation
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